The purpose of this proposed research is to determine, as precisely as possible, the clinical and behavioral significance of variation in the human karyotype. Eleven thousand infants from five cities who have been followed from birth in a collaborative study on cerebral palsy and mental retardation will be studied at the time of their final clinical evaluation at age seven. Since the physical findings, intellectual and emotional development of these children have been determined ad recorded on magnetic tape, correlations between variations in the karyotype and clinical parameters, such as mental retardation can be carried out without additional data acquisition. In addition, the available data may permit evaluation of possible etiologic factors leading to aneuploidy, as well as an assessment of the possible clinical significance of Q, G and C polymorphism and determination of racial and other population differences in the frequency of each polymorphism. The primary reason for selecting this group is their inclusion at birth in a prospective study and the availability of a large amount of information about them.